Alternator RPM

[nicks67camaro]

I am running an internally regulated alternator. The pulley is 2 1/2 inches. When I was timing my motor I saw the belt moving towards the bracket. I don't throw belts but my buddy had a 3 inch pulley that slowed the alternator down. Does anyone know where I can buy a new pulley or an application with a 3 inch pulley that will work?

Thanks Nick

[HILROD]

I got a pulley from a Camaro resto house. I think the application is from a 68 Z28.

[Z-man]

Can you afford lower amps?

[HILROD]

The amps put out would not lower. The charging would be somewhat less at lower rpm. The factory's would not have installed these if they didn't work. Maybe a Moroso or other pulley might be worse, but I've used a bunch of these GM reproduction pulleys, with no ill effects.

[nicks67camaro]

the car almost never idles. for the most part the engine will run between 3500 and 5500 rpm if I hammer on it then they get to 6500. So low RPM charging won't be an issue.

[Z-man]

The amps put out would not lower. The charging would be somewhat less at lower rpm. The factory's would not have installed these if they didn't work. Maybe a Moroso or other pulley might be worse, but I've used a bunch of these GM reproduction pulleys, with no ill effects.

Amps = charging, so the amps definitely will be lower. He didn't mention what alternator but it could have been an old one from '67. He also didn't mention what electrical accessories were being used on the car. The old alternators are barely adequate for what people are using them for now - some original alternators are rated at 40 amps. But that's at full speed (greater than 5000 rpm alternator speed). At idle, an alternator like this will not be charging at all. Check out this link. Alternator Theory You can see that a 40 amp alternator is putting out 0 amps at idle and less than 10 amps at 2000 rpm. If you have halogen headlights, you will be discharging the battery at idle. If you slow down an alternator like that, you may never charge the battery properly.

However, it sounds like this isn't a problem for nick, since he never idles!

[nicks67camaro]

I'm not sure how many amps the alternator is but I know its internally regulated I bypassed that external regulator as for accessories electric fan, fuel pump, 6al, I never had issues with charging. If I don't slow the alternator down then maybe use a guide of some sort or idler pulley? any ideals there?

[6'9"Witha69]

If you are concerned with belt throwing or the apparent slack you see in the wiggling of the belt, a larger pulley is not the answer. A deep groove pulley will aid in preventing belt throwing, but so will adequate alignment of the alternator pulley to the rest of the pulleys. Mounting hardware is hardly accurate from company to company. With my current mounting setup (mainly factory) and a 12SI I have 1/8" shims on the lower bolt at the head and 3/32" shims on the upper bolt between the bracket and 12 o'clock tab to properly align the pulleys. This in conjunction with a Z28 style deep groove pulley eliminated belt throwing, the wobble you describe and kept my charging system fully functional.

[nicks67camaro]

Its the wobble that concerns me. When belt gets the wobbles at higher RPMs I can see some belt material deposted on the heads. I know the belt is lined up good. Where can I buy one of those deep groove pulleys.